hw/riscv/sifive_e: Fix inheritance of SiFiveEState

hw/riscv/sifive_e: Fix inheritance of SiFiveEState

SiFiveEState inherits from SysBusDevice while it's TypeInfo claims it to
inherit from TYPE_MACHINE. This is an inconsistency which can cause
undefined behavior such as memory corruption.

Change SiFiveEState to inherit from MachineState since it is registered
as a machine.

Fixes: 0869490b1c ("riscv: sifive_e: Manually define the machine")

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220922075232.33653-1-shentey@gmail.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>